Single ended forward type DC to DC converters require special circuitry to periodically reset the core of the power transformer, since the single switch applies energy to the transformer winding, and hence to the core in one direction only. To maintain a flux balance and prevent the core of the transformer from drifting into saturation, it must be actively reset in each cycle of operation during a nonconducting period of the power transistor switch. To counteract the flux excursion into saturation most reset circuits reset the core magnetizing flux to a zero level and therefore only a unipolar flux swing is utilized.
A DC to DC converter also frequently includes a snubber circuit to reduce switching losses in the power switch during turn off. The loss reduction benefits of the snubber circuit become more critical as the frequency of switching increases since the energy loss in the switch due to turn off is relatively constant per each cycle of operation of the power switch. Hence, as modern converters move to higher operating frequencies, the importance of the snubber circuit increases. These circuits are also operative to reduce the occurrence of voltage spikes across the power switch and thereby reduce its voltage stress and also reduce radiated emission due to spike signal components. Snubber circuits may be either dissipative or nondissipative depending on whether it transfers energy back to the power train or dissipates it.
Meeting the above requirements requires that added circuitry be included in the power train and control circuitry of the single ended forward type converter. This adds to the cost and complexity of the overall circuit and the accompanying increase in component count is detrimental to the overall reliability of the converter.